Support for wireless access between a correspondent node and a mobile device over the Internet is outlined in an Internet Engineering Task Force (IETF) proposal entitled “IP Mobility Support,” C. E. Perkins—Editor, Request for Comments 2002 (October, 1996; hereinafter “Mobile IP”). By utilizing Mobile IP, each mobile device is always identified by a fixed home address and associated home agent, regardless of its point of attachment to the Internet. Packets sent to a mobile device, from a correspondent node, are directed to the home agent. If the mobile device is away from home, the home agent forwards packets within an IP-in-IP tunnel to an assigned care-of address registered with the mobile device. Mobile IP does not effectively support micro-mobility, that is, handoffs of a mobile device between base stations, each of which covers only a very small geographic area. This is because each handoff of a mobile device to a base station not attached or linked via a node hosting the home agent requires the mobile device to notify the home agent of its associated care-of address regarding the mobile device's new point of attachment. Therefore, the use of Mobile IP results in messaging and signaling delays and inefficient packet delivery paths to the mobile device.
When the mobile device is in its home network (i.e.—the same network in which the mobile device's home agent is located), packets destined for the mobile device are intercepted by the home agent. The home agent routes the packets as normal IP packets and sent to the Local Area Network to which the mobile device is normally attached. Therefore, Mobile IP does not support any mobility within the local subnet. If a mobile device changes its point of attachment within a local subnet, the change must be managed by either link layer modification techniques, or by broadcasting packets destined to the mobile device to all base stations attached to the local subnet. Managing the link layer may result in unacceptable delays and packet loss while broadcasting packets to all base stations is an inefficient use of bandwidth.
Recently an extension to the Mobile IP protocol emerged in a draft Internet Engineering Task Force (IETF) proposal entitled “Route Optimization in Mobile IP,” C. E. Perkins—Editor, Internet Draft—Work in Progress (November, 1997). The route optimization extension proposes a means in which packets may be routed from a correspondent node to a mobile device away from home without first being forwarded to a home agent. Route optimization extensions provide a means for the correspondent node to cache a binding associated with the mobile device and then tunnel packets directly to the care-of address indicated in that binding, thereby bypassing the mobile device's home agent. Utilizing the proposal, packets are forwarded from an old base station foreign agent to a new base station foreign agent to reduce disruption during handoff. However, a mobile device's care-of address is nonetheless changed each time the mobile device is handed off between base stations. Although route optimization is proposed as a scheme for improvement in micro-mobility, route optimization still requires undesirable notifications to the home agent and correspondent node for each handoff of the mobile device. Such frequent notification not only increases the amount of control traffic generated, but also places an unnecessary processing burden upon a fixed host which may be providing services to hundreds of fixed and mobile hosts. Until notification of a handoff is completed to the home agent and correspondent node, packets destined for the mobile device are forwarded from the old base station foreign agent to the new base station foreign agent. During the required round trip messaging time between the home agent and the correspondent node, packets follow an inefficient delivery path resulting in disruption to user traffic.